1. Field of the Invention
This invention relates to a transmission equipment including an interface for transmitting ETHERNET (trade mark) packet data in LAN (Local Area Network), etc. as a user network interface (UNI). Particularly, this invention relates to a transmission equipment for transmitting variable length ETHERNET packet data in a PON (Passive Optical Network).
2. Description of the Related Art
A PON system according to the related art is explained.
FIG. 12 shows a block configuration chart for explaining an optical communication equipment, its communication method and a system in which its control program is written disclosed in Japanese Unexamined Published Patent Application Hei 11-98151.
In FIG. 12, the optical communication equipment includes a station equipment 111 and a subscriber equipment 113. The station equipment 111 is connected to an external work station 112, and the subscriber equipment 113 is connected to a terminal 114.
The station equipment 111 has a function for changing band (band period or time band or time period) allocations dynamically. By this function, an unutilized band is shared among a plurality of subscribers who are members of band unassurance service instead of band assurance service for communications with the station equipment 111 in the PON system.
In this configuration, the subscriber equipment 113 includes a PDS (Passive Double Star) terminator 131 for terminating an interface with the station equipment 111, a terminal interface terminator 133 for terminating an interface with the terminal for the band unassurance service in a user side, a memory 132 for storing packet data which are converted between the PDS terminator 131 and the terminal interface terminator 133, and a memory controller 134 for measuring a stored data amount in the memory 132 and sending a request for transmission to the PDS terminator 131 when it is necessary to send a signal to the station equipment through the PDS terminator 131.
Meanwhile, the station equipment 111 includes a PDS terminator 121 for terminating an interface with the subscriber equipment 113, a controller 125 for terminating an interface with the external work station 112, which sends control information, and for distributing necessary control information to each of function blocks in the equipment, a subscriber information storing unit 124 for storing information on a subscriber who has applied to use a shared band (band period) in the control information received from the controller 125, a packet analyzer 123 for receiving the information on the subscriber from the subscriber information storing unit 124 and sending subscriber ID (Identification Data) and a polling instruction to the PDS terminator 121, and a time division switch (TSW) 122.
Operations of this system are explained.
The packet analyzer 123 sends the subscriber ID and the polling instruction to the PDS terminator 121, and receives a transmission request 151 and the subscriber ID from the concerning subscriber equipment 113. When the packet analyzer 123 receives the transmission request from the subscriber, the packet analyzer 123 sends a transmission permission signal 152 to the concerning subscriber equipment 113 queuing to transmit to the station equipment in the shared band period. Then, the packet analyzer 123 receives a packet signal returned from the subscriber equipment 113.
The packet analyzer 123 analyzes a packet length signal written in a packet overhead (LLC (Logical Link Control) part) in a first packet signal received from the subscriber equipment 113, and determines a time period to be occupied by the concerning subscriber equipment 113 based on the packet length. Then, the packet analyzer 123 sends the transmission permission signal 152 to the subscriber equipment 113 indicating the time period to be occupied, and receives a packet signal from the subscriber equipment 113.
The PON system according to the related art is configured as above stated. When a parent station allocates bands (band periods) for transmission directed to the station terminal to a plurality of child stations, the parent station sends subscriber ID information and polling instruction information to an arbitrary child station, and receives transmission request information and subscriber ID information from the concerning subscriber equipment. Further, when the parent station receives the transmission request information, the parent station sends the transmission permission signal to the concerning subscriber equipment, and receives the packet signal from the concerning subscriber equipment sequentially. Further, the packet analyzer in the parent station analyzes the packet length signal written in the packet overhead (LLC part) in the first packet signal received from the subscriber equipment, and determines the time period to be occupied by the concerning subscriber equipment based on the packet length. Then, the parent station sends the transmission permission signal indicating the time period to be occupied, and receives the packet signal from the subscriber equipment. As stated, complex processing is necessary in the system according to the related art.